How XIV handles a building power failure
anthonyv 2000004B9K Comments (2) Visits (9118)
I received a question the other day about how the XIV interacts with a customers building UPS.
So I thought I would share my answer with you.
The XIV has two separate line cords (there is an option to have four line cords but I am trying not to complicate this). This means the clients building power provides the XIV with two separate power sources.
As long as one of those two line cords provides input power, then the XIV will continue to operate normally.
If both power sources stop supplying input power then the client is not providing any electricity to the XIV (none at all).
This would suggest the clients computer room has suffered a severe building facility failure and that all of their other equipment has lost power too.
In this situation the XIV will continue to operate normally for 30 seconds on battery power, waiting in the hope that the clients power will come back on at least one of the two line cords.
If after 30 seconds, the XIV has not detected the return of any input power, it must take action to ensure it does not flatten it's internal UPS batteries. So it performs a graceful shutdown and powers itself off. Why wait only 30 seconds? The main reason is brown-out protection. If the client loses power for 20 seconds and then returns power, and does this recursively, they could progressively flatten the battery to the point where the XIV may not be able to gracefully shut down. This is not desirable, so the 30 second timer is a good compromise.
Overall this design allows the client the greatest levels of availability and data protection.
In terms of site EPO, the XIV does not have an EPO switch or interface, because the XIV design has a strict requirement to perform a graceful shutdown prior to power off.
If the client wants to manually power the machine off, they could instead issue a CLI or GUI command to the machine to request shutdown.
Shutdown takes about 30 seconds to complete because the machine needs time to destage cache and meta data to disk prior to shutting down the Linux OS that runs on each module.
So how do you power the XIV back on?
Just press the On switch on each of the three UPS modules (preferably all at once).
So how do you manually power the XIV off?
Always use the xCLI or XIV GUI to shut the XIV down. There are power off buttons on each XIV UPS, but these should be covered by a plate and never used (if they are not covered up, please contact IBM to have this done). We don't use these buttons as they don't let the modules shutdown gracefully.
If you launch an xCLI session from the XIV GUI, issue the following command and then respond to the prompts:
If you want to script the command then you need a script that looks like this:
xcli -m 192.168.30.91 -u admin -p adminadmin shutdown –y
If you choose to use emergency=yes then you may cause data loss, which is clearly not a good idea.
We add the -y parameter because the shutdown command is normally interactive. Clearly this assumes you have not changed the default password ( which is also not a good idea).
The GUI of course also has a shutdown option (that will give you some warning prompts as well):